Inductance unit



Oct. 6, 1953 A, s, KHOURl 2,654,861

INDUCTANCE UNIT Filed June 4, 1948 Patented Oct. 6, 1953 INDUCTANCE UNIT Alfred S. Khouri, Milwaukee, Wis., assignor to Globe-Union Inc., Milwaukee, Wis., a corporation of Delaware Application .l' une 4, 1948, Serial No. 31,009

Claims.

This invention is an nductance unit having substantially fixed resonant frequency characteristi-cs and a ,method of making the same.

The inductance unit of the present invention is rendered substantially self -com-pensating in respect to ambient temperature changes by so correlating the temperature coefficient of dielectric constant of the material of which the coil form is made to the temperature coefficient of expansion thereof, that the increase of inductance with increasing temperature is substantially compensated for by the decrease in interturn capacity.

One object of the invention is to provide an inductance unit of the character described which will have substantially fixed resonant frequency characteristics and accurate re-trace characteristics.

Another object of the invention is to provide an inductance unit of the character described comprising a coil form made from ceramic material having a negative temperature coeflicient of dielectric constant such as rutile, various ceramic titanate combinations including magnesium, calcium, and strontium titanates, and the like.

Another object of the invention is to provide an inductance unit having a coil form of ceramic material with a negative temperature coeiiicient of dielectric constant, which form is provided with a spiral conductor receiving groove so that a continuous conductor may be deposited within the groove to insure that substantially all of the interturn capacity of the coil is through the material of the coil form.

Another object of the invention is to bond the coil of an inductance unit of the character described to the ceramic coil form so that the coil and the coil form move together during eXpansion and contraction due to temperature changes.

These and other objects of the invention will become apparent from the following specication read in connection with the accompanying drawings wherein preferred forms of the invention have been illustrated.

In the accompanying drawings:

Fig. l is a diagrammatic view of a circuit sho-We ing the inductance unit of the present invention incorporated therein,

Fig. 2 is a view partly in section showing apreferred form of the invention, and

Fig. 3 is a similar View showing a modified form of the invention,

Fig. 4 is a -top plan View `of a flat type spiral coil form of inductance unit made in accordance with theY present invention,

Fig. 5 is a sectional view taken on the line 5-5 of Fig. 4, and

Fig. 6 is a sectional View similar to that of Fig. 5 vbut of a modified form of flat coil form having a groove in which -the conductor is deposited.

In describing the present invention, it is convenient to refer to a resonant circuit such as shown in Fig. l which includes an inductance Lo having distributed capacity Cd, and a capacity Cc. For a circuit such as represented in Fig. 1 and in which the total inductance may be represented by LT, and the total capacity by CT, the

Thetcrardifrerentia1 of F is n LT F dLT r T dF---2- T--z CT (3) In general, both Cr and LT will be functions of temperature, lthat is they are subject to change .due to changes in ambient temperature, and

dF -O (5) Hence, substituting in (4) there results LT u CT Assuming that substantially all the inductance of the vcircuit is localized in the coil, a consideration of the last given formula shows that LT/dt is the temperature coefficient of inductance of the coil and dCT CT/dlf is the temperature coeilicient of capacitance of the electric conductor follow the coil form in expansion and contraction movements thereof and in order to conne the interturn capacity of the unit to the material of the coil form, the coil form is preferably formed with a spiral groove in its surface and the conductor is deposited in the groove preferably on the bottom wall thereof, and is bonded to the coil form so as to of necessity follow the coil form in its expansion and contraction movements.

Referring to Fig. 2 of the drawings, there is shown a coil form 2U made of ceramic material such as rutile, or various combinations of titanates, and the like, the coil form being substantially cylindrical in form and hollow. The exterior cylindrical surface of the form is provided with a spiral groove or thread 2l, on the bottom wall of which is deposited a continuous coating of conductor 22 such as silver, copper, or the like. The coating is preferably bonded or mechanically locked to the surface of the form 20, on the bottom wall of the groove 2l in order to insure that the conductor 22 will follow the form in movement due to expansion and contraction. The spiral groove or thread 2| is preferably dimensioned in respect to depth so that the conductor 22 is confined substantially to the groove and has no substantial part thereof projecting above the external surface of the form whereby to insure that substantially all of the interturn capacity between adjacent convolutions of the conductor is through the material of the form. The metal conductor 22 may be deposited on and bonded to the bottom wall of the spiral groove k2l by any suitable means or method such as electroplating, a Schoops gun, or the like.

Although the form of the invention shown in Fig. 2 is preferred because of the enhanced temperature compensation realized by confining the metal coating or conductor within the spiral groove as shown, it is also possible to deposit the conductor film in the form of a spiral ribbon 23 directly upon the cylindrical outer surface of a coil form 24 as shown in Fig. 3. In this form of the invention, it is also preferable to mechanically bond or otherwise secure the spiral ribbon 23 to the outer surface of the form 24 in order that the conductor 23 will follow substantially the expansion and contraction movements of the coil form 24. Due to the fact that some of the interturn capacity of adjacent convolutions of the ribbon 23 in that form of the invention shown in Fig. 3 is through the air, or other surrounding medium, the compensating effect due to variations of temperature will not be as complete in this form of the invention as in the form of the invention shown in Fig. 1. However, the compensation will be substantial and in many instances fully adequate to meet specifications.

From the foregoing it is apparent that the inductance unit La can be made self-compensating when used by itself in a circuit without an external capacitor such as Co of Fig. l'. If, however, the coil is to be used in a circuit with an external capacitor as C0 and wherein the temperature coefficient of capacitance of the external capacitor is zero, then (la) becomes 6 However, it should be noted that under these circumstances the temperature coeflicient of dielectric constant of the coil form must needs be greater' in the ratio which gives rise to three possible conditions:

(1) (f-TCO?) in which Tod of (17) win be negative and realizable by using a coil form within the teaching of the present invention,

(2) if a: To0 than To.i of (17) will have to be zero, and as taught in Ehlers Patent 2,398,088 of April 9, 1946, ceramic material mixtures may be readily formed which have zero temperature coefficients of dielectric constant.

(3) If a To0 Tod of (17) will have to be positive and a ceramic coil form of the type described herein will serve no purpose.

The foregoing derivation of formulae proceeding from Formula 7 pertain to an inductance unit of cylindrical form and including a single layer helical or solenoid form of coil. However, the same advantages emphasized in respect to the cylindrical form of inductance may be realized with a flat coil form having a spiral coil mounted thereon as shown in Figs. 4, 5, and 6. Thus, as shown in Fig, 4, the unit may comprise a substantially flat, co-planar` base 25 of ceramic material having a negative temperature coeiicient of dielectric constant as previously referred to herein, which base may be round, square, or any other desired contour, and on which is deposited a flat spiral coil 26 in the form of a thin metallic ribbon. The ribbon coil 26 is bonded to the surface of the base 25 by electro-deposition, Schoops gun, or the like, to insure that the ribbon follows the base in its movement of expansion and contraction, due to changes in ambient temperature. Preferably the upper surface of the base 25 is provided with a spiral groove 2'? in which the ribbon 25 is deposited and bonded to the bottom wall thereof, the groove 2E being of a depth suiiicient to completely house the ribbon as shown in Fig. 6. If desired, the groove E may be substantially deeper than the thickness of the ribbon, so that the upper surface of the ribbon lies below the upper surface of the form similaito the manner shown in connection with the cylindrical form of coil, in Fig. 2.

It can be shown that flat spiral inductors made by bonding a metallic conductor, in the same manner and to the same class of ceramic bodies as hereinbefore described, onto the surface of temperature variation, will provide la circuit of substantially fixed resonant frequency in the race of ambient temperature changes.

Iclaim:

1. A self-compensating inductance coil comprising a substantially cylindrical coil form of ceramic material having a negative temperature coefficient of dielectric constant substantially equal in value to but of opposite sign to its temperature coeflicient of expansion and a conductor disposed spirally about said coil form and anchored to the coil form to cause the conductor and coil form to move together during movements of expansion and contraction due to temperature changes.

2. A self-compensating inductance coil comprising a substantially cylindrical coil form of ceramic material having a negative temperature coeilicient of dielectric constant substantially equal in value to but of opposite sign to its temperature coeiiicient of expansion, a spiral groove formed in the surface of said coil form, a continuous conductor deposited within said groove With al1 portions thereof disposed within the connes of said groove whereby substantially all of the interturn capacity 0f adjacent convolutions of the conductor is through the material of the coil form and means for anchoring the conductor to the coil form to cause the coil and coil form to move together during movements of exnegative temperature coeiiicient of dielectric constant substantially equal in value to, but of opposite sign to, its temperature coeilicient of expansion and a conductor disposed spirally upon said coil form and iixed theretoto cause the conductor and coil form to move together during expansion and contraction due to temperature changes.

4. A self-compensating inductance coil comprising a coil form of ceramic material having a negative temperature coeiilcient of dielectric constant substantially equal in value to but of opposite sign to its temperature coeflicicnt of expansion, a spiral groove formed in the surface of said coil form, a continuous conductor deposited within said groove and xed to the coil form to cause the conductor and the coil form to move together during expansion and contraction due to temperature changes all portions of said conductor being disposed within the connes of said groove whereby substantially all of the interturn capacity of adjacent convolutions of the conductor is through the material of the -coil form.

5. A self-compensating inductance coil comprising a flat, co-planar coil form of ceramic material having a negative temperature coefficient of dielectric constant substantially equal in Value to but of opposite sign to its temperature coeiicient of expansion, a spiral groove formed in one flat surface of said coil form, a continuous conductor deposited within said groove and fixed to the coil form to cause the conductor and coil form to move together during expansion and contraction due to temperature changes, all portions of said conductor being disposed within the confines of said groove whereby substantially all of the interturn capacity of adjacent convolutions of the conductor is through the material of the coil form.

6. A self-compensating inductance coil comprising a substantially flat-co-planar coil form of ceramic material having a negative temperature co-eicient of dielectric constant substantially equal in value to but of opposite sign to its temperature coefficient of expansion and a conductor disposed spirally upon one at surface of said form and anchored thereto to cause the conductor and coil form to move together during expansion and contraction due to temperature changes.

'7. The method of forming an inductance unit which is self-compensating in respect to temperature changes which comprises selecting and proportioning the ingredients of a ceramic mix including at least one compound having a negative coefficient of dielectric constant chosen from the group consisting of magnesium titanate, calcium titanate, and strontium titanate, and titanium dioxide, which mix will provide in a coil form made therefrom a -negative temperature coefficient of dielectric constant and a positive Ytemperature coefcient of expansion that are numerically equal but oi Opposite sign, mixing the chosen ingredients, forming a ceramic coil form from said ceramic mix, depositing on the coil form an electrical coil the interturn capacity of which is restricted to the material of the coil form, and bonding said electrical coil to the coil form substantially throughout the length of said coil so that the coil and coil form move together as the result of expansion and contraction due to ambient temperature changes.

8. The method of forming an inductance unit which is self-compensating in respect to temperature changes which comprises forming a ceramic mix including at least one compound having a negative temperature coeiiicient of dielectric constant chosen from the group consisting of magnesium titanate, calcium titanate, and strontium titanate, and titanium dioxide, said compound being present in an amount to provide in a coil form made from said mix a negative coeiiicient of dielectric constant substantially equal to but of opposite sign to its temperature coeicient of expansion, making a ceramic coil form having said characteristics from said mix, depositing on said coil form a continuous conductor in the form of a coil, coniining the interturn capacity of adjacent convolutions of said coil substantially to the material of the coil form, and constraining the conductor coil, substantially throughout its length, and the coil form to move together in their movements of expansion and contraction under ambient temperature changes.

9. The method of forming an inductance unit which is self-compensating with respect to ternperature changes which comprises forming a ceramic mix including at least one compound having a negative temperature coeiiicient of dielectric constant chosen from the group consisting of magnesium titanate, calcium titanate, and strontium titanate, and titanium dioxide, said compound being present in an amount to provide in a coil form made from said mix a negative temperature coeilicient of dielectric constant substantially equal to but of opposite sign to its temperature coelicient of expansion, making a generally ilat, spirally grooved ceramic coil form having said characteristics from said mix, depositing on said coil form within said groove a continuous conductive layer in the form of a coil, confining said coil substantially within said groove, so that substantially all of the interturn capacity of adjacent convolutions of said coil will be through the material of the coil f'r, intending the9111111 1113j-' atiauy through: v111111115"iengt111-1 the Aconfermi so' they move to: g'ether in therfnovement of expansiontand con? traction due to lambient temperature changs.

10. The method of forming an inductance unit whichY is self-compensatir With' rspect to terniialtu chang'e Which (":c'impise's forrning a mix ineluling' atleast one compound lng ngative temperature coefficient of difVA per Vllifr'e' coefnclent ofmdielectrc constant Sub? tantially eguai to'ilit 'o1 opposite' Sign to' its tn'- p erajtiu'eA coef'cli'tlof expansion, makinga cylinh dic groote@ ceramic coil form hvingwslaigiy charactri' i''is fron said. ni1, vsgind'ng ensei@ @bi1 ,fm with@ ,Sad gob'v a `olfti' enlayer in ,th'elflolrfr'iv of coil, coii'n n Said $1691?, Sfiht 1,111@ @www "pmyo'fae jacentconvolutlen. Qi Saidlwil. b'. Ph'h the. material. Qf, the 1191i, epfl. @ending the c1111 eubtenially, thfwgheuiii .lngtl t0' th @Q11 19H11 S9111e1-m91e19eethe1. @their movements 11` 221115611111011., eesicentractioh du@ t0 bient 11211111121211111112, A

elifeemeeeseting induteneilipf. the character descrjijoe Q in ,c 1 a1 rn r'` 2m Whereinthefpon- 111191101 1191111121111 1119. b otwril ,Sereqef tf1@ Spiral glooyewhereyte .91.10W ,the @111111611155 of thevcoil forinhin its*Y egpanei'on and contraction due1Q,.-t@1n1Qe1f21t111re.1/21riat r1,Amm c ,121 A self:commen@atineinduqtan C011. $11111 as @escribeme .11211111..1-111herei11-1he Conductor isY bondedubstantally, throughout, ,its ,length t0 the. coil. ,form whereby. the `Acon.111.111.1161, is i, 01511,-, strained to I nove ,with the coil torrnmaswthe latter expands and contracts due to temperature varia- .tionS.., 1 3. In combination Wthua capacitor o fppredetermined Value; a temperature compensated in.- ductance unit operatively, connected theretoand comprising a coil form of ceramic material hav; ing a conductor coil mounted thiereonV and, fxed thereto, so asA to move, therewith substantially throughout its length during movements of exriefen-1111115111 the i111 ef peff STAT'S AE' Dat@ Scho'op :s Feb'. I9, 1918 Nov. Il; 1924 MayV 233-i 1933 1: Jur'l 21,- 1938 l 193e 194'6 Y 1 Mair.' 9, 192118 noemen PATENTS Country Date Great Britain Mar. 24; 1941 Y OTHER REFERENCES Niunber Polydo'roir 2,394,391

Martotricz White 1 2,437 ,345 

